Normal tissues and organs contain a population of stem cells capable of self-renewal and recapitulation of the organ or tissue. Cancer stem cells (CSCs) were first detected in patients with acute leukemia and more recently in a variety of solid tumors. These cells have been characterized and isolated for study by phenotype based on cell surface antigens (CD44+ CD24−, CD133, etc.) and by functional activities including enhanced efflux-pumping of a Hoechst dye and over-expression of aldehyde dehydrogenase1 (ALDH1). In general, these tumor CSCs share common characteristics including self-renewal, ability to induce tumors at low cell numbers, ability to produce tumors composed of differentiated and heterogeneous cell profiles, low rates of cell division, gene expression profiles that differ from their more differentiated cell counterparts and resistance to standard chemotherapy and radiation.